This 9TR was not made at the Portsmouth factory, but in Mexico. It is a Rockwell 8R gone green! This variant was made exclusively for the 'True Value' stores in the U.S. Rockwell's main market channel was through retailers at around this time, and they made variants for various stores, like the House of Fraser in the U.K. (see the 18F) and Sears and Roebuck in the States (see the 8M). This one is unusual in that it retains both the Rockwell styling and the Rockwell logo---only the colour has changed. This unit has its I.C. stamped 7546 (week 46 of 1975).
There is no manual for the 9TR but it behaves identically to the 8R, The 8R manual can be found on the manuals page.
Try it out---it works!